This invention relates to magetic recording disks for use in perpendicular magneic recording systems, such as rigid disk drives.
Perpendicular magnetic recording, wherein the recorded bits are stored in a perpendicular orientation in the media, is considered to be a promising path toward ultra-high recording densities in magnetic recording rigid disk drives. While perpendicular magnetic recording rigid disk drives have not yet been commercially realized, several types of perpendicular magnetic recording media have been proposed.
The most widely reported type of perpendicular media is a cobalt alloy (e.g., CoCr or CoCr with one or more of Pt, Nb and Ta) xe2x80x9cgranularxe2x80x9d layer grown on a growth-enhancing sublayer that induces the crystalline C-axis to be perpendicular to the plane of the layer, so that the layer has strong perpendicular magnetic anisotropy. This type of media is called xe2x80x9cgranularxe2x80x9d because the individual grains are only weakly exchange coupled laterally.
To achieve granular Co alloy perpendicular recording media with good signal-to-noise ratio (SNR) at high recording density, it is believed that very good crystalline orientation of the Co alloy is necessary. The perpendicular orientation of the Co alloy C-axis with respect to the film plane has usually been obtained by grain-to-grain epitaxial growth of the hexagonal (HCP) Co alloy thin film to an oriented HCP sublayer of (0002) crystalline texture or a face-centered-cubic (FCC) crystalline underlayer of (111) crystalline texture. Titanium (Ti) and Ti90Cr10 are often cited as the best sublayers for this purpose, although other materials, such as Pt, CoO/Pt and nonmagnetic CoCr35 have been used. See Y. Hirayama et al., xe2x80x9cDevelopment of High Resolution and Low Noise Single Perpendicular Recording Media for High Density Recordingxe2x80x9d, IEEE Trans. Magn., Vol. 33, No. 1, p. 996 (January 1997). An underlayer structure of Ti/CoZr has also been suggested, wherein the CoZr layer is said to reduce the surface roughness of the bare glass substrate on which it is formed. See I. S. Lee et al., xe2x80x9cRole of a paramagnetic amorphous CoZr seed layer in CoCrPt/Ti perpendicular recording mediaxe2x80x9d, J. Appl. Phys., Vol. 85, No 8, Apr. 15, 1999, pp. 6133-6135.
Materials with a B2 body-centered-cubic (BCC) crystalline structure, such as Ni50Al50, have been described as good sublayers for supporting the known Cr underlayers onto which horizontal or longitudinal Co alloy media is formed, as described in U.S. Pat. No. 5,693,426. These B2 type sublayers serve as good templates for the  less than 110 greater than  Cr orientation which causes the C-axis of the Co alloy media to be in-plane. Thus, the combination of Ni50Al50 with Cr and Cr-based alloy underlayers results in the formation of longitudinal media.
To obtain high SNR of the Co alloy perpendicular media, the grain size of the media needs to be made small enough to obtain the high resolution required for sharp magnetic bit transitions. Thus what is needed is a perpendicular magnetic recording media with an underlayer structure that produces Co alloy media with small grain size but yet does not significantly reduce the desired crystalline structure.
The present invention is a perpendicular magnetic recording disk with an underlayer structure that causes the magnetic layer to have perpendicular magnetic anisotropy and high SNR. The underlayer structure comprises a B2 type BCC material, such as the binary alloys NiAl, RuAl and RuTi, as an underlayer, and a Ti or TiCr alloy sublayer formed directly on the underlayer. The magnetic layer, such as a CoCrPt alloy, is deposited directly on the sublayer. The magnetic layer has perpendicular magnetic anisotropy due to the sublayer yet excellent SNR because of the smaller grain size of the sublayer material formed directly on the B2 type underlayer.
For a fuller understanding of the nature and advantages of the present invention, reference should be made to the following detailed description taken together with the accompanying figures.